SAE J661 Brake Lining Quality Test Procedure (Chase Test)

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SAE J661 — Brake Lining Quality Control Test Procedure (The "Chase Test")

SAE J661 core purpose is to establish a uniform laboratory procedure for securing and reporting the friction and wear characteristics of brake linings under controlled, repeatable conditions. It formulates a unified laboratory test method to evaluate the safety performance, friction properties and wear behaviors of brake linings. The test results serve as core evidence for in-factory quality control of brake lining manufacturers and incoming quality inspection for buyers of brake linings. It is also commonly known as the Chase Test in the friction material industry.

Test principle and methods:

This test simulates actual braking conditions via a rotating metal test drum rubbing against brake lining specimens under controlled load, speed and temperature. By continuously monitoring friction force, drum temperature, specimen thickness and weight changes throughout the whole test cycle, it quantitatively assesses three core performances of brake linings: basic friction stability, friction fade (performance decline under high temperature), friction recovery (performance restoration after cooling), and material wear resistance. All tests are conducted consecutively without interruption to ensure data authenticity and consistency.

A square specimen of brake lining material is pressed (loaded) against the outer circumference of a rotating cast-iron drum under controlled conditions.

The drum is heated and cooled in a prescribed cycle, simulating the temperature swings a brake sees in service.

Throughout the cycle, friction force is measured → the coefficient of friction (μ = Friction Force ÷ Normal Load) is computed at multiple temperature points.

The key material behaviors probed are:

Friction level at ambient / warm conditions ("normal" friction)

Thermal fade — how much μ drops as temperature rises (fade /test)

Recovery — how well μ recovers when temperature drops again (recovery /test)

Wear — thickness and mass loss after repeated cycling

This is a coupon-level material test, not a full brake assembly or vehicle dynamometer test. It isolates the friction material's intrinsic behavior from variables like caliper geometry, rotor design, or vehicle inertia

Test Specimen — Dimensions & Preparation

Parameter	Specification
Size	25.4 × 25.4 mm (1.0″ × 1.0″) square — taken from center of friction material, equidistant from edges.
Working surface	Radius must match the test drum radius (contoured).
Back face	Flat; excess thickness machined off the backside.
Nominal thickness	≈ 6 mm measured at center.
Surface prep — pre-ground linings	Remove ≥ 0.3 mm, ≤ 0.5 mm from working face.
Surface prep — as-molded (unground)	Remove 1.0–1.2 mm to fully eliminate resin-rich surface skin.
Thin linings (< 5 mm)	Minimize backside machining — just enough to produce flatness.
Handling rule	Working surface must not be touched by hand or contaminated.
Specimen Burnishing	Before formal testing, burnish specimens at 308 rpm and 440 N load for no less than 20 minutes, with the maximum drum temperature limited to 93 °C (200 °F). The contact area between the specimen and drum must reach over 95%.

Test Equipment required for the SAE J661 Chase Friction Test of Brake Lining:

Chase Friction Materials Test Machine
Test drum	Nominal diameter 279.4 mm (11.0″); usable ID range 277.4–279.9 mm; made of cast iron; three thermocouple holes at specific depths (2.55 / 3.05 / 3.55 mm from new surface)
Drum temperature measurement	Welded thermocouple → coin-silver slip rings → silver-graphite brushes → high-impedance recorder/display; accuracy ±2% FS
Drum heating	Electric resistance heater; controlled heating rate: heat from 82°C→221°C in ~10 min
Drum cooling	Back-side-only forced-air cooling; controlled cooling rate: from 371°C→93°C in ~10 min
Friction force measurement	Load cell / mechanical linkage; accuracy ±2% FS
Drum rotational speed	Motor-driven; target ≈ 411–417 rpm (based on 279.4 mm nominal drum); accuracy ±2% FS
Specimen thickness & mass	Micrometer (to 0.01 mm) + analytical balance (to 0.001 g)
Auxiliary Tools	320-grit abrasive paper, clean flannel/white soft paper for drum surface treatment, and dial indicators for wear measurement.

Key Test Parameters

All parameters are fixed and must be strictly followed during continuous testing:

Parameter Category	Specific Values & Requirements
Standard Drum Rotation Speed	411 rpm (benchmarked on nominal drum diameter 278.5 mm under loaded state)
Main Test Load	660 N (used for baseline, fade, recovery and wear tests)
Burnishing Load	440 N; Pre-run load: 220 N
Initial Drum Temperature Range	Baseline test: 82–93 °C (180–200 °F); Initial wear test: 88–99 °C (190–210 °F)
Temperature Threshold for Fade Tests	1st fade: 288 °C (550 °F); 2nd fade: 343 °C (650 °F)
Maximum Duration for Fade Tests	10 minutes (test stops when either temperature limit or time limit is reached first)
Wear Test Temperature Range	193–216 °C (380–420 °F)
Specimen-Drum Clearance (Non-contact state)	0.3–0.4 mm
Measurement Precision	Weight: accurate to milligram; All measuring systems (temperature, friction, speed): ±2% full scale

General Test Stipulations

All test procedures must be performed continuously without interruption.

The test drum shall only be cooled from the back side; cooling air and heaters are switched on/off as required by each test segment.

For intermittent loading tests, the friction coefficient is defined as the value at the end of each loading period.

After each test, polish the drum surface with abrasive paper (final polishing with 320-grit sandpaper) and remove dust completely.

Record all data in the unified master log sheet and draw performance curves on the master plot sheet.

Complete Test Procedures

The whole test includes 11 sequential steps:

Baseline Test 1: Run 20 cycles of 10-second loading (660 N) + 20-second unloading at 411 rpm. Keep drum temperature at 82–93 °C; turn off cooling air for the last loading cycle.

First Fade Test: Cool the drum naturally to 82 °C, then apply 660 N load and turn on the heater for continuous dragging. Stop when temperature hits 288 °C or duration reaches 10 minutes. Record friction force every 28 °C (50 °F) increment starting from 93 °C, and record the time to reach 288 °C.

First Recovery Test: Turn off the heater, turn on cooling air, and maintain 411 rpm. Apply 10-second 660 N load and record friction force when the drum cools to 260 °C, 204 °C, 149 °C and 93 °C successively.

Second Wear Measurement: Repeat the initial wear measurement method.

Wear Test: Conduct 100 cycles of 20-second loading (660 N) + 10-second unloading at 411 rpm. Maintain drum temperature within 193–216 °C throughout the test.

Third Wear Measurement: Cool the drum to 88–99 °C, then repeat the initial wear measurement.

Second Fade Test: Cool the drum to 82 °C, apply load and turn on the heater. Stop when temperature reaches 343 °C or duration hits 10 minutes. Record friction force at every 28 °C increment and the time to reach 343 °C.

Second Recovery Test: Cool the drum at 411 rpm. Record friction force by 10-second loading when temperature drops to 316 °C, 260 °C, 204 °C, 149 °C and 93 °C.

Baseline Test 2: Repeat the operation of the first baseline test.

Final Wear Measurement: Repeat the initial wear measurement.

Final Thickness & Weight Measurement: Measure and record specimen thickness (3 axial points) and weight, following the initial measurement rules.

SAE J661 Brake Lining Quality Test Procedure (Chase Test)

Industry Fields & Applications

Brake lining / friction material manufacturers	Incoming raw material QC, batch release, formulation R&D, process change validation
Tier-1 brake suppliers & OEMs	Purchasing inspection of bought-in linings; supplier qualification
Aftermarket / relining shops	Verifying that replacement linings meet the labeled edge-code claim
Regulatory & certification bodies	Referenced in state/provincial environmental marking schemes (CA, WA brake copper rules via SAE J866)
Standards ecosystem	Cross-referenced by GB 5763 (China), ISO 26867, and others as a recognized friction-material screening method

Related Test Standard:

Related Standard	Relationship to J661
SAE J866 (Friction Coefficient Identification & Environmental Marking System)	The most direct sibling — J866 consumes J661 test data to assign the two-letter edge code (e.g. EF, FF, GG) that is physically stamped on the lining's edge. First letter = normal μ (avg at 93/121/149/204°C on 2nd fade curve); Second letter = hot μ (weighted avg of 10 defined points across fade & recovery). J866 also carries the environmental mark (copper content class A/B/N + year)
SAE J2975	Method for measuring Cu & other elements in brake friction materials — referenced alongside J866 for environmental compliance
SAE J2522 (AK Master / inertial dyno)	Complementary full-brake-assembly inertial dynamometer test — operates at vehicle-system level, whereas J661 is coupon-level
SAE J670	Vehicle dynamics terminology (brake performance context)
ISO 26867	International equivalent / counterpart — Road vehicles — Brake linings — Friction behaviour assessment— harmonized philosophy with the Chase-type approach
GB/T 29064	Road vehicles.Brake lining friction materials.Friction behaviour assessment method for automotive brake systems
GB 5763	Chinese national standard for automotive brake linings — references SAE J661-style methodology for classification/testing

Brake lining friction and wear testing machine, also known as CHASE friction testing machine. Used to test the friction properties of friction materials in the braking system, and is suitable for M1, M2, N1, 01, 02 types of vehicles using small sample bench tests.

Q1: What exactly is the SAE J661 test?

A: SAE J661 is a standardized laboratory test procedure (often called the "Chase Test") developed by SAE International. It evaluates the friction, wear, and thermal stability of brake lining materials using a specialized machine where a small square sample is pressed against a rotating cast-iron drum under controlled heating and cooling cycles.

Q2: Why is the SAE J661 test important?

A: It is important because:

It provides a consistent, repeatable way to compare brake lining materials from different suppliers or batches.

It helps detect thermal fade (loss of braking power when hot) and poor recovery—critical safety issues.

It supports quality control in manufacturing and supplier qualification.

The data is used to assign the SAE J866 edge-code (e.g., "FF", "GG") printed on brake pads/shoes, which informs mechanics and consumers about the material’s friction characteristics.

It enables rapid screening of new formulations without expensive full-vehicle testing.

Q3: What are the test specimens like?

A: Specimens are 25.4 mm × 25.4 mm (1"×1") squares cut from the center of a brake lining. They must:

Match the curvature of the test drum.

Have a flat back surface.

Be prepared by removing a specified amount of surface material (to eliminate resin-rich layers).

Never be touched on the working surface to avoid contamination.

Q4: Can SAE J661 results predict real-world braking performance?

A: No. SAE J661 explicitly states that its data cannot reliably predict full braking system performance. Real-world braking depends on many factors: caliper design, rotor type, vehicle weight, tire grip, etc. J661 only characterizes the material’s intrinsic friction and wear properties under controlled lab conditions.

Q5: Why is the test called the "Chase Test"?

A: It is named after Robert S. Chase, who developed the original test machine and methodology in the 1950s to standardize brake lining evaluation.

Q6: What is the biggest misconception about SAE J661?

A: That a "higher friction code = better brakes." In reality, the optimal friction level depends on the vehicle design. Too high μ can cause noise, judder, or premature rotor wear. J661 simply classifies the material—it does not prescribe what is "best."

Q7: Why do we need to grind the working surface of the test specimen?

A: Grinding removes the surface resin impregnation layer and damaged surface material formed during production. For machined linings, grind 0.3–0.5 mm; for raw demolded linings, grind 1.0–1.2 mm, to ensure the test reflects the true performance of the bulk friction material.

Q8: Can I touch the working surface of the specimen directly by hand?

A: No. Hand contact or foreign contamination will alter surface friction characteristics and lead to inaccurate test results

Q9: Why must the test drum only be cooled from the back side?

A: This rule standardizes the heat dissipation condition of the drum, ensuring consistent temperature change rates across all tests and eliminating variable factors that affect friction and fade data.

Q10: Can I pause or interrupt the SAE J661 test halfway?

A: No. All test steps must be conducted continuously without interruption to guarantee the consistency of material temperature, surface state and performance data.

Q11: What is a friction fade test in SAE J661?

A: It is a high-temperature drag test. The specimen runs continuously under load while being heated. The first fade test stops at 288 °C or 10 minutes; the second stops at 343 °C or 10 minutes. It assesses whether friction force drops sharply at high temperatures.

Q12: What is a friction recovery test?

A: After the fade test, cool the drum gradually. Apply short-time loading at several set temperature points and record friction force. It evaluates how well friction performance recovers after the brake lining cools down from high temperature.

Q13: Why do vehicle manufacturers require suppliers to provide SAE J661 test reports?

A: To verify that purchased brake linings have stable friction performance, good high-temperature resistance and wear resistance. It avoids defective brake parts from being assembled onto vehicles and controls overall braking system reliability.

Q14: What problems will happen if a brake lining fails the SAE J661 fade test?

A: The material will suffer severe friction loss under high working temperature, resulting in insufficient braking force, extended braking distance and even complete brake failure, which brings serious traffic safety hazards.

Q15: Why do friction test data differ greatly between repeated tests on the same sample?

A: Common causes: Unpolished test drum surface, contaminated specimen working surface, inconsistent heating/cooling rate, incorrect specimen installation, or failure to meet the 95% contact area requirement during burnishing.

Q16: What if the target temperature is not reached within 10 minutes during the fade test?

A: The test stops when the 10-minute time limit is reached. Use the friction values at the 10th minute to complete data statistics and coefficient calculation as required.

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